Do sports drinks really give your workout an extra edge? A recent study of the performance-enhancing claims of more than 100 fitness products says probably not. In fact, of the hundreds of such claims identified in product advertisements and websites, researchers couldn’t find a single one that was backed by solid scientific evidence.

For the study, researchers at the University of Oxford looked at advertisements for sports drinks, oral supplements, footwear, clothing and fitness devices like wristbands and compression sleeves in 100 general interest magazines and the top 10 sport and fitness magazines in the U.K. and the U.S. The team also searched the websites of any product making claims to enhance athletic performance or improve recovery, seeking references for scientific studies supporting these claims.

The researchers found 235 magazine ads for sports products, of which 54 made claims to improve performance or recovery. Only three products provided references; many simply offered celebrity athlete endorsement instead. The 53 websites the researchers examined contained 431 performance-enhancing claims for 104 products, with a total of 146 references. More than half of the sites provided no references at all.

The researchers then contacted 42 companies for references that couldn’t otherwise be found, and heard back from 16, nine of which offered additional material. Among the companies that didn’t provide usable references, two, Panache and New Balance, said they were unwilling to share their research; one, Nike, offered a video of its product in use and said it was “sufficient”; and one, Merrell, pointed to the work of a researcher but didn’t say whether the company had any research on its actual product.

After sifting through the available references, the researchers discarded half for being unfit for scientific appraisal; they pointed to books without clinical studies, nonexistent studies, conference abstracts or online surveys without data, or nonhuman studies, such as a study of the effects of different diets on rat metabolism published in 1930. Of the 74 studies that could be evaluated, the team found that only three were of high quality and low risk for bias. Notably, all three reported no significant effects of the intervention studied.

Victor Katch, a professor of kinesiology at the University of Michigan Ann Arbor who was not affiliated with the current research but studies the validity of fitness products, says the findings aren’t surprising. “We are in a culture where testimonial evidence and talking heads have a lot of power and sway, especially in areas where people have little knowledge,” he says. “People want to do something about their fitness and wellness and they’re willing to give products a chance. Almost every week there’s a new diet or fitness book out, and they’re all nonsense.”

The marketing of sports products has become a multibillion dollar industry, the authors note, and each year consumers increasingly buy into the claims of performance-enhancing products, especially so-called energy drinks. But the “current evidence is not of sufficient quality to inform the public about the benefits and harms of sports products,” the authors write.

To be fair, there may yet be evidence, not included in the new study published in the journal BMJ Open, that backs some of the products’ claims. The authors also acknowledge that while they attempted to include a representative sample of products in their study, it’s possible that the ones they analyzed were “on the worst end of the spectrum.” The scientists note further that they didn’t give manufacturers much time to respond to their requests for more information.

But, by and large, many experts in the field agree that the evidence shoring up sports product claims is thin. “There is a need to improve the quality of the research conducted in this area and its reporting, and a move towards using systematic review evidence across the board for decision-making,” the authors conclude.

Unfortunately, many manufacturers are unwilling to put in the time, money or effort required for solid research, says Katch. “[As experts in the field], we have a responsibility to offer proper information to the public. If we don’t, no one will. It’s very unregulated,” he says.

For consumers left wondering which fitness products are worth the money and which aren’t, the answer is that there isn’t enough evidence to say. But for the average American, it’s less important to try to boost performance than it is to just get moving, says Katch. If you want to know whether your fancy running shoes will help shave seconds from your time, you’ll need to get out there and hit the pavement.